Grease composition

ABSTRACT

A mineral oil grease which is resistant to separation by centrifugal force is provided by using as the sole thickening agent either polyethylene having a number average molecular weight of from about 1,500 to about 3,000 or a combination of said polyethylene with a small amount of a lithium higher fatty acid soap.

United States Patent [191 Miller et al.

[ 51 May 20, 1975 GREASE COMPOSITION [75] Inventors: James E. Miller, Griffith; Reuben A.

Swenson, Whiting, both of Ind.

[52] US. Cl 252/41; 252/59 [51] Int. Cl. Cl0m 5/14; ClOm 5/10 [58] Field of Search l. 252/41, 59,39

[56] References Cited UNITED STATES PATENTS 2,627,938 2/1953 Frohmader et al. 252/59 2,833,718 5/1958 Morway et al 252/39 3,083,160 3/1963 Agius et al 252/29 3,271,311 9/1966 Morway et a1 i 252/41 3,290,244 12/1966 Polishuk et al. 252/41 3,293,179 12/1966 Bertocsk 252/41 3,396,108 8/1968 Caruso 252/18 Primary ExaminerDelbert E. Gantz Assistant Examiner-I. Vaughn Attorney, Agent, or Firm-Edwin C. Lehner; Arthur G. Gilkes; William T. McClain 5 7 ABSTRACT A mineral oil grease which is resistant to separation by centrifugal force is provided by using as the sole thickening agent either polyethylene having a number average molecular weight of from about 1,500 to about 3,000 or a combination of said polyethylene with a small amount of a lithium higher fatty acid soap.

10 Claims, No Drawings GREASE COMPOSITION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to grease compositions which are resistant to separation of the thickening agent from the base lubricating oil during use under centrifugal force conditions.

2. Description of the Prior Art Large rotary compressors, operating at speeds from in the range of 5,000 to about 15,000 rpm, are wellknown devices used in the gas compress on art. Coupling of the drive shafts of the rotary compressor and prime mover, such as a steam turbine, is effected by means of high speed flexible gear couplings which are provided with gears for vertical and lateral movement during operation. Lubrication of such gear couplings is extremely important because such compressors are continuously operated for extended periods of time. The use of sealed couplings to permit the use of liquid lubricating oils as the lubricant is not satisfactory because of alignment problems between the driving and driven shafts. Maintenance of the liquid seal under misalignment conditions is therefore extremely difficult. Consequently, most of the gear couplings now in use are of the unsealed type which require the use of a grease as the lubricant. A grease suitable for this latter type of high speed coupling lubrication needs to be heavy enough to be packed into the couplings by hand and be able to lubricate the coupling satisfactorily for periods of many months of continuous operation. Conventional greases, i.e., greases thickened by metal soaps and solid fillers, such as graphite and molybdenum disulfide, separate into their components in this service and frequent replacement is required, some times as often as every three months. Thus, a grease is needed that will not separate under the centrifugal forces developed in the operation of the aforesaid high speed flexible gear couplings.

SUMMARY OF THE INVENTION It has been discovered that low molecular weight polyethylene can be used either alone or in combination with a small amount of lithium soap as the sole thickening agent for mineral lubricating oil to form greases which are resistant to centrifugal separation and suitable for use as the lubricant for unsealed high speed flexible gear couplings.

Commercially available low molecular weight polyethylenes suitable for use in the present invention have a number average molecular weight in the range of from about 1,500 to about 3,000, preferably 2,000, and a melting or softening point in the range of from about 210 to about 240F.

The greases of the present invention consist essentially of a mineral lubricating oil having a viscosity in the range of from about 130 to about 200 SSU at 210F containing as the sole thickening agent for said oil either (a) from about 6 to about 10, preferably 7 8, weight per cent of polyethylene having a number average molecular weight in the range of from about 1,500 to about 3,000, preferably about 2,000, or (b) from about 6.5 to about 12 weight per cent of a mixture consisting of (i) from about 6 to about weight per cent of polyethylene having a number average molecular weight in the range of from about 1,500 to about 3,000 and (ii) from about 0.5 to about 2, preferably about 0.85 to about 0.9, weight per cent of a lithium soap. Greases formed with the polyethylene alone have a drop point of about to about F. Since the operating temperatures of the couplings are generally within the range of about 150 to about 200F, it is desirable to improve the thermal stability of the centrifugally stable greases of this invention. It has been discovered that, when a small amount of a conventional lithium soap grease thickener is incorporated with the aforesaid polyethylene during the manufacture of the grease of this invention, the drop point of the resultant grease is raised to above 200F without adversely affecting the centrifugal stability of the grease. The greases of this invention initially have an NGLI (National Lubricating Grease Institute) grade consistency of about 3 or 4 and after working will have an NGLI grade of about 0 to I. This softening characteristic of the grease is highly desirable for it can be easily handled during packing of the couplings and thereafter satisfactorily lubricate the gear couplings at their operating temperatures without separation of its components and thus provide extended operation of the gear couplings without any loss in lubrication.

The mineral lubricating oil used in the greases of this invention can be any of the conventional petroleum lubricating oils having a viscosity in the range of about 130 to about 200 SSU '(Saybolt Seconds Universal) at 210F. A preferred petroleum lubricating oil is a bright stock having a viscosity of about 180 195 SSU at 210F.

The lithium soap employed in the present invention is well known in the art. The term lithium soap used herein and in the claims refers to the soaps or salts which are formed by the reaction of lithium hydroxide with fats or higher fatty acids such as stearic, hydroxystearic, palmitic, oleic and the like. In place of the substantially pure fats or acids, mixtures of fats or fatty acids such as those obtained from the various fatty oils such as cotton seed oil, rapeseed, mineral oils, fish oils and the like can be used. The saturated fatty acids such as those derived from hydrogenated oils of vegetable, animal and marine origin can also be used. A preferred lithium soap is the lithium salt of a mixture of hydrogenated castor oil and hydrogenated fish oil fatty acids.

When desired, conventional grease additives such as extreme pressure agents, oxidation inhibitors, corrosion inhibitors and the like can be effectively incorporated in the grease compositions of this invention.

In preparing the greases of this invention, the polyethylene is simply added to the base lubricating oil at a temperature of about 250F and held with agitation for a period of about 30 minutes to assure complete solution of the polymer in the oil. If the lithium soap is included, it is combined with the base oil prior to addition of the polyethylene to the heated oil. After the polyethylene is dissolved, the mixture is cooled to about 200F and any supplementary additives such as extreme pressure agents, antioxidants and rust inhibitors are then incorporated. Thereafter, the mixture is cooled, with or without stirring, to about 175 F and packaged. No milling of the grease mixture is required to form the grease compositions of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Centrifugal stability of the greases described herein was determined by centrifuging at 150F a sample of the grease in a centrifuge operating at 4,300 rpm. The relative centrifugal force (RCF) imposed on the grease in this test is equivalent to 3,870 G. A gear coupling operating at 7,000 rpm has an RCF of about 3,700.

In the exemplary formulations set forth in the following Table, a conventional lithium soap grease, containing 7 percent lithium soap of hydrogenated castor oil and hydrogenated fish oil fatty acids (the ratio of castor oil to the fatty acid being was used to provide the indicated amounts of lithium soap in the greases of this invention.

The low molecular weight polyethylene used in preparing the illustrative greases of this invention has a 2. The composition of claim 1 wherein the molecular weight of said polyethylene is about 2,000.

3. The composition of claim 2 wherein said thickening agent is about 7 weight percent polyethylene.

4. The composition of claim 2 wherein said thickening agent is a mixture of about 7 weight percent polyethylene and about 0.85 to about 0.9 weight percent lithium soap.

5. The composition of claim 4 wherein said lithium soap is a lithium salt of a mixture of hydrogenated castor oil and hydrogenated fish oil fatty acids.

6. 1n the operation of centrifugal gear couplings wherein a solid lubricant is used to lubricate the gears in said coupling, the improvement comprising using as number average molecular weight of about 2,000 and id l bri ant the grease composition of claim 1. a softening point of about 220F and is available com- 7, In the operation of centrifugal gear couplings mercially under the trade name A-C Polyethylene 6. wherein a solid lubricant is used to lubricate the gears TABLE Formulation lngredients* l 2 3 4 5 6 7 Lubricating 0i|** 86 5 87 6 89 6 60.0 67.0 75.0 74.0 Lithium Soap Grease 30.0 20.1 12.6 12.4 Lithium Soap 2.1 1.4 0.88 0.87 A-C 6 polyethylene 6.9 7.0 5.0 4.5 8.1 7.0 6.9 Zinc dialkyldithiophosphate 36 3.6 3.6 3.6 3.2 3.6 3.6 Lead Naphthenate 1.8 1.8 l 8 1.8 1.6 1.8 1.8 Ortholeum 300*** 0.2 0.2 Phenyl-alphanaphthylamine 0.1 1 Zinc naphthenate 1.0 1.0 Penetrations:

Unworked 194 198 425 230 234 196 Worked, 60 strokes 326 332 479 360 352 333 339 &-QL L Unworked 4 4 3 3 4 Worked, 60 strokes l l 0 0 l 1 Hours Centrifu ed 48 72 24 72 72 48 Oil Separation, wt. 0 0 4.5 0 0 0 Drop Point, F 145 248 ln wt. 70. Petroleum bright stock having a viscosity of 187 SSU at 210F. Commercial antioxidant identified as a mixture of aromatic amines.

We claim: in said coupling, the improvement comprising using as 1. A grease resistant to separation by centrifugal said luubricant the grease composition of claim 2. force consisting essentially of a mineral lubricating oil 8. In the operation of centrifugal gear couplings having a viscosity in the range of from about 30 t0 wherein a solid lubricant is used to lubricate the gears about 200 SSU at 210F containing as the S016 thickenin said coupling, the improvement comprising using as ing agent for said oil either (a) from about 6 to about id l bri nt the c i i f l i 3, 10 weight per cent of polyethylene having a number av- 50 9, I the o eratio of ent if al gea o li erage molecular weight in the range of from about wherein a solid lubricant is used to lubricate the gears 1,500 to about 3,000 from bout 65 t0 a u 12 in said coupling, the improvement comprising using as weight per cent of a mixture consisting of (i) from aid l b i t th m iti f l i 4 about 6 to about 10 weight per Cent Of polyethylene 10. In the operation of centrifugal gear couplings having a number average molecular weight in the range wherein a solid lubricant is used to lubricate the gears of from about 1,500 to about 3,000 and m about in said coupling, the improvement comprising using as 0.5 to about 2 weight per cent of a lithium higher fatty id l b i t th iti f l i 5, acid soap. 

1. A GREASE RESISTANT TO SEPARATION BY CENTRIFUGAL FORCE CONSISTING ESSENTIALLY OF A MINERAL LUBRICATING OIL HAVING A VISCOSITY IN THE RANGE OF FROM ABOUT 130 TO ABOUT 200 SSU AT 210*F CONTAINING AS THE SOLE THICKENING AGENT FOR SAID OIL EITHER (A) FROM ABOUT 6 TO ABOUT 10 WEIGHT PER CENT OF POLYETHYLENE HAVING A NUMBER AVERAGE MOLECULAR WEIGHT IN THE RANGE OF FROM ABOUT 1,500 TO ABOUT 3,000 OR (B) FROM ABOUT 6.5 TO ABOUT 12 WEIGHT PER CENT OF A MIXTURE CONSISTING OF (I) FROM ABOUT 6 TO ABOUT 10 WEIGHT PER CENT OF POLYETHYLENE HAVING A NUMBER AVERAGE MOLECULAR WEIGHT IN THE RANGE OF FROM ABOUT 1,500 TO ABOUT 3,000 AND (II) FROM ABOUT 0.5 TO ABOUT 2 WEIGHT PER CENT OF A LITHIUM HIGHER FATTY ACID SOAP.
 2. The composition of claim 1 wherein the molecular weight of said polyethylene is about 2,000.
 3. The composition of claim 2 wherein said thickening agent is about 7 weight percent polyethylene.
 4. The composition of claim 2 wherein said thickening agent is a mixture of about 7 weight percent polyethylene and about 0.85 to about 0.9 weight percent lithium soap.
 5. The composition of claim 4 wherein said lithium soap is a lithium salt of a mixture of hydrogenated castor oil and hydrogenated fish oil fatty acids.
 6. In the operation of centrifugal gear couplings wherein a solid lubricant is used to lubricate the gears in said coupLing, the improvement comprising using as said lubricant the grease composition of claim
 1. 7. In the operation of centrifugal gear couplings wherein a solid lubricant is used to lubricate the gears in said coupling, the improvement comprising using as said luubricant the grease composition of claim
 2. 8. In the operation of centrifugal gear couplings wherein a solid lubricant is used to lubricate the gears in said coupling, the improvement comprising using as said lubricant the composition of claim
 3. 9. In the operation of centrifugal gear couplings wherein a solid lubricant is used to lubricate the gears in said coupling, the improvement comprising using as said lubricant the composition of claim
 4. 10. In the operation of centrifugal gear couplings wherein a solid lubricant is used to lubricate the gears in said coupling, the improvement comprising using as said lubricant the composition of claim
 5. 